cracked heat exchanger/Do I need a new furnace?

Hello
Thank you for being here!! I have just spent over an hour reading everything that would pertain to my problem.

Problem: I believe I have have a cracked heat exchanger. Flames rolling back, luke warm air coming out of vents.

a tech came out and was able to remove (by putting nontool metal stick up into opening and banging/tapping on it) soot build up. quite a bit fell out half a bucket.

Since then my indoor temp ok, producing heat and thermostat ok. But last night set at 66 and by morning house temp. 63 Furnace ran all night but not able to keep up and provide correct temp.

House built in 1889, wood siding, no insulation, with crawl space.

Equipment: SynyderGeneral packaged heating and cooling unit, purchased in 1989, and most are non insulated ducts.

Unit #PGHA 036G 100 AIN

Serial # R894000050

Draft meter installed in 1992 - by previous owner

My husband had worked for a heat & air co. before and has taken it apart and cleaned burners etc. also installed or placed the following:

Spark Ignition System
Thermo Couple

Our next thing to change is the Limit switch.

My Question is do I hunt for a heat exchanger (if I can find one) If that is the problem? Or do I replace the whole unit?

I am looking for the best cost way to go. Our house is currently on the market for sale. I have heard that a home warranty Ins. that you purchase would be helpful in this situation.

Thank You lsudden

 

You need to 1st confirm whether or not it is cracked.

If it is just replace the whole thing. If you were to find a heat exchanger "very doubtful" for a 20 year old furnace the cost would out weigh the value.

 

It doesn't sound like your repairman has done the job properly for you, at least the way you describe the work done.

What it sounds like is that the problem was, and still may be, a heat exchanger plugged with soot. A plugged heat exchanger will prevent the combustion gasses from moving through the furnace up up the vent and outdoors, causing them to back out the front of the furnace instead.

Your repairman should have disassembled the furnace and cleaned the heat exchanger completely, which usually requires some somewhat specialized brushes and such to get into obscure parts of the heat exchager to do the job properly.

Banging on the heat exchanger with a metal rod may be a start but doesn't do the job adequately by itself.


The most common cause of a heat exchanger plugged with soot is dirty burners --- when did your husband do that job?

Once the heat exchanger is clean it can be inspected for cracks and holes. Did the repairman say he's found cracks or holes in the heat exchanger? That might be a reasonable reason for not expending more time to do the cleaning process correctly.

 

I was right there with the repair man checking and asking questions. No visable cracks he just said it was bad because the flames shoot back. But he did remove all the soot that he could by THAT method. no more soot was coming out. He did have the panel off and burners out etc. to reach up into the heat exchange.

Thank YOu Lsudden

 

I was right there with the repair man checking and asking questions. No visable cracks he just said it was bad because the flames shoot back. But he did remove all the soot that he could by THAT method. no more soot was coming out. He did have the panel off and burners out etc. to reach up into the heat exchange.

Thank YOu Lsudden

 

Based on what you've described, there is no reason to suppose the job was done properly, especially with the fames continuing to back out of the furnace, a classic symptom of a plugged heat exchanger.

 

I don't want to hyjack this thread, but I was curious about something. So after 14 years at this facility I am going to ask. What causes the heat exchanger to plug up with soot? I keep the filters changed religiously, Also I see it as an almost impossibility to clean the heat exchangers on my furnaces, as they are buried way inside and after taking it apart its completely plugged and I really see no way to clean these. Payne/Rheem 350MAV, getting ready to install the new furnace.

It is possible that some of these appliances were set wrong from day one, I lost a hot water tank, and all the apartment stoves were set up for natural gas and not propane, I fixed those problems. I wish I could take some training on how to set pressures and tell if the furnaces were burning properly. I suppose that after 14 years, some of these furnaces are reaching their end of life cycle.

It would seem that sooting would be caused by burning too rich, which would be caused by too large of orifices or the gas regulators being set wrong. Any thoughts are greatly appreciated. Thanks in advance.

 

Yes, that will certainly cause sooting if bad enough. That's why changing out a gas valve isn't a good DIY project, because a new gas valve has to have the pressure set properly.

The most common cause of sooting though are dirty burners.

Taking the burners out is usually not adequate for cleaning up a sooted heat exchanger, which typically involves more disassembly of the furnace. And until you've cleaned the furnace properly, you can't really begin to do a good job of inspecting the heat exchanger for cracks and holes.